1. Field of the Invention
The invention relates to a method of manufacturing an electromagnetic deflection unit for a cathode ray tube, which unit comprises a field deflection coil consisting of two parts, a line deflection coil consisting of two parts and an annular core of a magnetizable material surrounding the two coils, the two parts of the field deflection coil being wound in a hollow funnel-shaped coil support.
2. Description of the Related Art
Such a method is known from EP No. 0 102 658 A1. (See also DE No. 2 940 931.)
Cathode ray tubes have a neck-shaped portion one end of which accommodates an electron gun and the other end of which continues into a flared, for example, trumpet or cone-shaped part contiguous to a screen. An electromagnetic deflection unit surrounds the neck-shaped portion and engages the flared part or is provided at a short distance therefrom. In the case of a colour picture tube this deflection unit must be capable of deflecting the electron beams towards the corners of the screen while maintaining convergence. This means that both the horizontal deflection field and the vertical deflection field must have a very special distribution. To realize this, in the known method, a coil support is provided which at each of its ends has an annular flange having guide grooves accurately distributed on its circumference, in which grooves the longitudinal segments of the coil turns terminate. It is then possible to control the wire distribution (and hence the field distribution).
Since in the known method the wires of the line deflection coil and those of the field deflection coil are both wound on the inside of one and the same coil support and are therefore situated close together at that area, there is a risk of ringing occurring between the line deflection coil and the field deflection coil.
Since only a limited number of grooves can be provided at the ends in the circumferences of the annular flanges, it may occur--depending on the coil design--that there are a number of grooves through which turn segments of the line deflection coil and of the field deflection coil are passed. During winding the field deflection coil turns are first positioned in these grooves and thereafter the line deflection coil turns. In addition to the risk of ringing there is also the risk of breakdown between the line deflection coil and the field deflection coil.